JPH0775922B2 - Radial tire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pneumatic radial tire, and more specifically, it is possible to improve tire performance by utilizing the shape change of the carcass due to the internal pressure filling of the carcass. The present invention relates to a radial tire that can be suitably used for vehicles such as buses and light trucks.

[Prior art and its problems]

To improve the cut resistance and wear resistance of tires,
Conventionally, it has been proposed to use a rubber having good cut resistance and wear resistance for the tread portion, and to use a rubber compound having a high impact resilience to improve fuel efficiency. However,
When cut-resistant and abrasion-resistant rubber is used, high-speed durability, fuel economy, etc. are reduced. If a rubber compound having high impact resilience is used, the fuel economy is improved, and the wet grip performance is deteriorated such as traction performance.

Therefore, it is also known that the tread rubber is divided into two parts in the radial direction of the tire into a cap rubber and a base rubber, a rubber compound having cut resistance and wear resistance is used for the cap rubber, and a low hysteresis rubber is used for the base rubber.

However, although there are some improvement effects by these measures, the cut resistance and wear resistance are drastically reduced from the middle period of use when the wear of the cap rubber has advanced, and the rigidity of the tread part is reduced, so the basic performance is reduced. That is, other performance such as steering performance is impaired.

Therefore, the present inventor, as a result of various studies on the shape of the carcass line of the carcass, rather than the rubber characteristics,
Utilizing the deformation of the carcass line due to the internal pressure filling, the preferable rigidity in the range to the tread portion and the side wall portion,
The present invention has been completed by finding that strain can be imparted and the tire characteristics can be obtained.

[Object of the Invention]

The present invention provides a radial tire (hereinafter simply referred to as the tire of the present invention, or a tire) that can be improved in cut resistance and wear resistance without impairing other performances and can be preferably used particularly for trucks and buses. Has an aim.

[Means for solving problems]

The present invention relates to a carcass (1) having a steel cord arranged in a radial arrangement by folding back from a tread portion (5) to a side wall portion at a bead core (7) (7 ') of a bead portion.
And a belt layer (3) using a steel cord disposed inside the tread portion (5) and outside the carcass (1) and inclined at a small angle in the tire circumferential direction, a radial tire having the nominal application of the tire. The radius of curvature TR1 of the outer surface of the tread portion (5) in the tire meridian section at the time of mounting on the rim and filling the air pressure corresponding to 5% of the nominal maximum air pressure and the nominal maximum air pressure are filled. The ratio of the outer surface of the tread portion (5) to the radius of curvature TR2 in the tire meridional section at the nominal maximum internal pressure is 1.20 ≦ TR2 / TR1 ≦ 1.50, and at the carcass line (11) at the internal pressure of 5%. Curvature radius CR1 in the range from shoulder to buttress
And the radius of curvature in the range from the shoulder to the buttress in the carcass line (12) at the nominal maximum internal pressure
The ratio with CR2 is 0.70 ≤ CR2 / CR1 ≤ 0.95, and when the internal pressure is 5%, the distance RX1 from the tire rotation axis YY 'of the intersection X1 between the carcass line (11) and the tire equatorial plane SS', and the nominal The carcass line (1
2) and the tire rotation axis YY ′ at the intersection X2 between the tire equatorial plane SS ′
From the distance RX2 to 1.000 ≦ RX2 / RX1 ≦ 1.005, and the intersection C1 where the carcass line (11) at 5% internal pressure and the radial line N1N1 ′ passing through the tread edge E1 at 5% internal pressure intersect An intersection point C2 where the radius RC1 from the tire rotation axis YY 'of the vehicle and the carcass line (12) at the nominal maximum internal pressure and the radius line N2N2' passing through the tread edge E2 at the nominal maximum internal pressure intersect
The ratio RC2 / RC1 to the radius RC2 from the tire rotation axis YY ′ is larger than the ratio RX2 / RX1, and the maximum tire width at nominal maximum internal pressure is the maximum tire width at 5% internal pressure. A radial tire characterized by being substantially unchanged.

In the tire of the present invention, the nominal maximum air pressure is JI.
It is the maximum value of air pressure in the air pressure-load correspondence table specified for each tire size by SD4202, and the nominal applicable rim is defined as the applicable rim in the same JIS, and when multiple rims are specified , Those in bold.

For example, a typical tire size for trucks and buses 1
0.00R20 14PR tires, approved rim 7.50V × when 20 to be mounted to fill the maximum air pressure 7.25 kg / cm ² for normal, ranging 400mm~600mm the unloaded condition tread curvature radius 180mm
It has a tread width of about 200 mm.

Further, with a uniform ground contact pressure distribution, in order to obtain a good grip and uniform wear, it is preferable to increase the tread curvature radius of the tire meridional cross section to have a flat profile,
Further, by adopting the configuration of the present invention, along with the magnitude of the absolute value of the radius of curvature of the tread, when the tire is filled with the nominal maximum air pressure at the nominal maximum internal pressure, the compressive strain acts on the tread crown portion rather than the tensile strain. The carcass line can be set to improve the cut resistance and wear resistance of the tread.

Further, with such a configuration, the lateral rigidity of the tread can be kept higher from the initial stage of use of the tire to the final stage, and steering stability of the vehicle is not impaired.

Further, since the rigidity of the tread portion is improved, the wet grip property and the traction performance are maintained, and the tread gauge can be made thin to reduce the weight of the tire.

An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 2, the tire T is disposed on the inside of the tread portion and outside of the carcass 1 as well as the carcass 1 from the tread portion 5 to the side wall portion and folded back at the bead cores 7 and 7 '. And the belt layer 3.

The carcass 1 comprises a carcass cord in a radial arrangement extending substantially in a radial direction, for example, a steel cord 1
The belt layer 3 is composed of a plurality of plies, and the belt layer 3 is composed of a plurality of plies composed of non-stretchable or low stretchable cords. The width BW of the belt layer 3 is the width TW of the tread portion 5
It is preferable to support the tread widely and surely within the range of 80% to 95%.

The cord of the belt layer has a small angle with respect to the tire circumferential direction in at least two plies, for example, a bias angle within the range of 10 ° to 30 °, and the upper and lower plies intersect each other to form a triangle structure. By forming it, the belt rigidity can be increased, which is advantageous for reinforcing the tread. For this reason, for example, when the three plies are directly overlapped with each other, the cords of the two plies have an angle with respect to the equatorial plane of the tire in the range of 10 ° to 25 ° which are equal in size and opposite in direction, and The cord of the third ply has a larger angle than the cords of the other two plies mentioned above, for example in the range of 40 ° to 70 °.

After making the belt layer a belt structure having such a high rigidity, a carcass having a deep relationship with the radius of curvature of the tread when inflated has focused on and obtained the following points.

As shown in Fig. 2, the rigidity of the remaining carcass parts, excluding the carcass and the reinforcement layer and the carcass at the top of the bead reinforced by the apex, which are tightened by the hoop effect of the strong belt structure, is compared. Low and low resistance to deformation.

This part has a shape close to the free equilibrium profile due to high internal pressure filling, and has a great effect on the meridional cross-sectional shape of the tread, that is, the profile.

Therefore, 5% of the nominal maximum air pressure shown by the broken line in FIG.
The radius of curvature CR1 of the shoulder portion of the carcass line 11 at the time of 5% internal pressure filling with the air pressure equivalent to is the nominal maximum internal pressure filling the nominal maximum air pressure that most closely approximates the free equilibrium profile 15 indicated by the chain line at the shoulder. Radius of curvature of "carcass line 12 on the shoulder" at
It is better than CR2 and the ratio CR2 / CR1 is usually in the range of 0.70 to 0.95. The "carcass line shoulder portion" and "shoulder portion carcass line" are defined as follows, buttress portion which is the upper portion of the sidewall portion from the so-called shoulder portion of the tire axial direction outer side portion of the tread. Is the range up to.

By setting in this way, it is possible to reduce the radius of curvature of the shoulder portion of the carcass line together with the filling with the internal pressure, to generate a preferable compressive strain in the tread portion as described later, and to improve the rigidity in the tread portion. As a premise, steel cords are used for the carcass and the belt, and when the carcass is deformed, for example, 5% so as not to change in the tire maximum width portion.
The maximum tire width W at that time and the maximum tire width W'at the nominal maximum internal pressure are set to the extent of 0.99W≤W'≤1.01W.

In addition, the carcass line is a curve connecting the middle positions of the thickness of the carcass, and the carcass line of the shoulder portion,
The radius of curvature CR1 and CR2 are defined as follows in this specification. In FIG. 10, (i) P1 is determined as an intersection of a carcass line 1 and a radial line NN 'which is a line segment parallel to the equatorial plane, that is, the tire equatorial plane SS', that is, a radial line passing through the tread edge.

(Ii) Equatorial plane SS 'parallel to the radial line NN' and from the radial line NN '
The intersection P2 between the radius line LL 'and the carcass line 1 having the same distance to is obtained.

(Iii) A radial line OO ′ parallel to the equatorial plane SS ′ and the radial line NN ′ passing through the point PO at the maximum width position of the carcass line 1.
The intersection point P3 between the carcass line 1 and the radial line MM 'that bisects between

The range between P2 and P3 is called the "shoulder carcass line", at each carcass line 11 and 12 at 5% internal pressure and nominal maximum internal pressure, inward in the radial direction of the tread edges E1 and E2 in each case. Radial line N1 passing through each tread edge E1, E2
It is determined as described above centering on N1 'and N2N2', respectively.

P1 is found at the intersection of the carcass line and the line segment NN 'passing through the tread edge parallel to the equatorial plane SS'.

The curvature radii CR1 and CR2 are the radii of arcs passing through the three points P1, P2 and P3.

Further, the carcass line will be described.

In FIG. 2, the carcass 1 has a bead core 7, 7 '.
And at points f and f '. The length from f to f'is the length between the bead wires of the carcass 1, and is the length determined by the outer contour dimension of the tire, the belt layer and the rubber gauge. The carcass 1 is made of steel cord together with the belt 3 and is arranged at 90 ° with respect to the equatorial plane. Therefore, even if the carcass 1 is filled with maximum air pressure, its length does not change much.

FIG. 1 shows a carcass carcass line 12 which is mounted on a nominal applicable rim (hereinafter referred to as a rim) and corresponds to an unloaded tire at the nominal maximum internal pressure, and an unloaded tire at 5% internal pressure. The carcass line 11 is shown.

The carcass touches the bead core at f and f ', and the tire equatorial plane
It intersects with SS ′ at intersections X1 and X2.

The tire is symmetrical with respect to the tire equator, and the length ff 'in the meridian section of the carcass 1 is twice the length fx from the contact points f, f'with the bead wire to the intersection points X1, X2 with the equatorial plane SS'. be equivalent to.

Here, a line segment that passes through the tread edge E2 at the time of the nominal maximum internal pressure and is parallel to the tire equatorial plane SS ′, that is, the intersection C2 indicating the intersection of the radial line N2N2 ′ and the carcass line 12, is the equatorial plane SS ′.
At an axial distance of AC2 from the tire rotation axis centerline,
That is, it is assumed that it is located at a radial distance RC2 from the tire rotation axis YY 'or the tire axis.

At this time, the radial line N1N1 'and the carcass line 11 passing through the tread edge E1 having a 5% internal pressure and parallel to the tire equatorial plane SS'
The intersection point C1 is the intersection point C2 in the case of the nominal maximum internal pressure,
The carcass line 11 is selected so as to come inward in the radial direction and inward in the axial direction.

The intersection C1 is shown in FIG. 1 when the axial distance AC1 from the tire equatorial plane SS ′ is smaller than the distance AC2. However, AC1 may be larger than AC2 or the same distance. The radial distance RC1 from the tire axis YY ′ is RC2
Make it smaller.

On the other hand, the belt layer 3 has increased rigidity as described above,
Because of the strong hoop effect, the intersection X2 between the carcass line 12 with the nominal maximum internal pressure and the equator plane SS 'is substantially the same as the intersection X1 between the carcass line 11 and the tire equator SS' when the internal pressure is 5%. It is better to set them at the same position. However, due to the elastic modulus of the rubber, variations in the finished angle of the cord, etc.,
The point X2 is the radial distance RX1 from the tire rotation axis YY ′ to the point X1.
0.5%, which is substantially 0.3%, is set to a small radial outward distance RX2. That is, the ratio is usually 1.0
00 ≦ RX2 / RX1 ≦ 1.005.

This ratio itself is no different from conventional tires.

In the present invention, the intersection point C2 at the nominal maximum internal pressure
The circumferential length 2πRC2 around the tire rotation axis rr ′ passing through (radius RC2) is greater than the circumferential length 2πRC1 around the tire rotation axis rr ′ passing through the intersection point C1 (radius RC1) when the internal pressure is 5%, Therefore RC2> RC1 and the radius RX2 and R
Make the ratio RC2 / RC1 larger than the ratio RX2 / RX1 with X1,
Therefore, the characteristic is that RC2 / RC1> RX2 / RX1.

RC2 / RC1 is usually set within the range of 1.005 to 1.020.

If RX1 = RX2 and RC1 = RC2, the radial distance from the intersection points C1 and C2 to the tire rotation axis YY 'does not change even if the tire is inflated, that is, neither the radius of curvature nor the strain of the tread surface changes. become.

If RX1 = RX2 and RC1> RC2, the tire rotation axis at intersection C1.
The radial distance RC1 from YY ′ is reduced to the distance RC2 after inflation, which helps reduce the radius of curvature of the tread surface.

That is, when RC2 / RC1 ≦ RX2 / RX1 is the carcass line of the conventional tire.

In this way, the internal pressure that restores the shape in the mold is 5%.
The range from the shoulder portion of the carcass line 11 to the buttress portion at the internal pressure is arranged radially below the carcass line 12 having the nominal maximum internal pressure that approximates the free balance profile. Therefore, it is not necessary to simply increase the length of the normal line from the tread edge E1 to the carcass line 11, that is, the shoulder rubber gauge B1. In addition, thicken the shoulder rubber gauge B1 to make the carcass line
If 11 is suppressed below the carcass line 12, the heat generation of the tire will increase due to the internal energy loss of the rubber in proportion to the gauge, and the high-speed durability of the tire will deteriorate.

Therefore, in the present invention, the tread curvature radius TR1 of the tread surface, which is the outer surface of the tread portion at the time of 5% internal pressure, is reduced so that the tread is parallel to the tire rotation axis Y-Y 'and at the tire equatorial plane SS'. Line segment TT 'tangent to the surface and tread edge E1
Radial length C1 'between and (hereinafter camber height C
1 ') is larger than that of conventional tires, so that the carcass line can be
11 may be arranged below the carcass line 12.

As described above, the tire in which the carcass line 11 having an internal pressure of 5% is arranged below the carcass line 12 having the maximum nominal internal pressure in the radial direction, the carcass line moves upward due to inflation and the carcass close to the free balance profile. Become a profile. As a result, in Figure 3, 10.00R20 14PR
As illustrated in the case of the tire having the tire size, the tire shape is largely deformed in the range from the buttress portion corresponding to 60% or more of the tire cross-sectional height to the tread portion.

Incidentally, in the tire having the conventional profile shown in FIG. 4, the tire shape is deformed substantially uniformly as a whole due to inflation.

The shape shown by the solid line in Figs. 3 and 4 is the maximum nominal air pressure (7.
25 kg / cm ² ) The outer surface shape when filled with a nominal maximum internal pressure of 5 kg is 7.25 kg / cm ² of the maximum nominal air pressure.
The outer contour shape of the tire when inflated to the air pressure of 0.36 kg / cm ² is modeled with gypsum.

The movement of the carcass line due to the pneumatic filling and the difference in the deformation of the tire outer contour shape affect the tension distribution of the carcass, and in the tire according to the present invention, from the buttress portion above the sidewall portion where the deformation amount is large to the shoulder portion of the tread. The tension of the carcass has increased over time,
The apparent rigidity is also large.

Similarly, since the carcass line has a larger amount of deformation (RC2-RC1) near the tread edges E1 and E2 than the amount of deformation (RX2-RX1) on the tire equatorial plane, compressive strain acts on the tread surface, Combined with the large rigidity of the part,
Lateral rigidity can be increased.

Further, the ratio of the radius of curvature TR1 of the tire meridional section of the outer surface of the tread portion at 5% internal pressure to the radius of curvature TR2 at the nominal maximum internal pressure is usually 1.20 ≦ TR2 / TR1 ≦ 1.50, and the tire shoulder Due to the large expansion in the portion, compressive strain can be applied to the shoulder portion.

With these, in addition to improving cut resistance and wear resistance,
It can improve driving stability.

Even if the air pressure increases, the carcass in the tire maximum width part hardly changes, and the tire maximum width W and the nominal maximum air pressure at the time of filling the air pressure equivalent to 5% of the nominal maximum air pressure at 5% internal pressure are The maximum tire width W at the time of filling at the nominal maximum internal pressure is preferably 0.99 W ≤ W '≤ 1.01 W, which, in combination with the carcass and belt layers being steel cords, contributes from the tread to the buttress. The above-mentioned deformation of the range up to the part is possible.

An important factor in the steering stability performance is cornering power. The cornering power is related to the rising gradient of the cornering force. With tires with high bending pressure such as truck and bus tires or tires using steel cords with high bending rigidity in the belt such as radial tires, with increase in lateral rigidity of the tread,
It is known that cornering power is increased.

In the case of a radial ply tire, since the lateral rigidity of the carcass is low, it is subject to torsional deformation due to lateral force, so that the shoulder portion tends to rise.

On the other hand, in the tire including the carcass line of the present invention, the lateral rigidity of the tread, which has a high contribution to the cornering power, is increased in the upper region of the carcass from the buttress to the tread portion.

A carcass line that increases the lateral rigidity by compressive strain acting on the tread contact surface is adopted.

As a result, even if a lateral force acts due to the addition of a slip angle to the tire and lateral deformation occurs, high cornering power can be exerted and excellent steering stability can be obtained.

In the tire of the present invention, a reinforcing layer composed of two or more nylon fiber cords crossing each other at a bias angle of 30 ° to 50 ° from the lower side wall portion of the maximum width to the bead portion is arranged, In addition, by adopting a triangular apex made of soft rubber and hard rubber and increasing the elastic coefficient, steering stability can be further improved.

Next, the rolling resistance is highest in the tread portion, especially in large tires for trucks and buses, which is close to 40%, and when the palletless portion is added, it is around 50%. Therefore, as described above, conventionally, a rubber compound having a high impact resilience has been used in order to reduce the internal energy loss of the tread rubber and reduce the rolling resistance, but in this case, a characteristic important for safety. Wet grip performance, which is one of the above, deteriorates.

On the other hand, the tire of the present invention improves rigidity by increasing the tension of the carcass from the buttress to the tread portion and appropriately changes the radius of curvature of the tread by inflating, so that the rubber accompanying the rolling of the tire The movement of the roller is reduced, and the energy consumption is reduced, so that the rolling resistance is reduced.

This not only does not impair wet grip performance and high-speed durability, but also improves steering performance, cut resistance, and wear resistance.

〔Example〕

For tire size 10.00R20 14PR, tires of Examples 1 and 2 and conventional technology (Comparative Examples 1 and 2) were prototyped, and changes in tread curvature radius, tread distortion, cut resistance, vertical deflection, rolling resistance, cornering force, and cornering force were measured. Vibration and riding comfort performance were measured.

The main profile specifications of both tires are shown in Table 1.

For both tires, the carcass 1 uses one ply in which steel cords (twist structure 7 × 4 / 0.175 mm) are arranged at 90 ° with respect to the tire equatorial plane, and belt 3 uses steel cords (twist structure 1 × 3 / 0.20 + 1 × 6 / 0.38 mm) with the tire equatorial plane, the first belt is arranged at 67 °, the second to fourth belts are arranged at 16 °, and the first and second belts are arranged next to the carcass layer in this order. The carcass profiles of the tested tires, called 2, 3, and 4 belts, are shown in FIG.

First, for these tires, the strain on the tread surface and the radius of curvature of the tread were measured, and then a tread rubber cut test was performed.

The results are shown in Table 2.

Next, as a result of investigating the relationship between the tread surface strain and the longitudinal spring constant or the cornering force, which is a measure of the riding comfort and steering stability of the tire, the tread surface strain is compressive strain as shown in Figs. 7 and 8. In comparison with the comparative example tire 1 in which tensile strain acts, the working example tire 1 of the present invention does not change the magnitude of longitudinal deflection, but the cornering force is 10%.
It shows high data. This is a reflection of the increase in lateral rigidity at the ground contact surface due to the large tension of the carcass ply acting from the buttress to the tread portion and the compressive strain in the tire axial direction.

From the above, it can be said that the riding comfort of the tire having the profile according to the present invention is the same as that of the conventional tire, but the steering stability is excellent. Similarly, the rolling resistances of tires were compared, but as shown in FIG. 9, the tire of Example 1 according to the present invention had a rolling resistance of 10% lower than that of the tire of Comparative Example 1 of the related art, and the tire fuel It shows that consumption is reduced considerably. This is because the tire of the present invention from the tire ground contact surface to the buttress portion has less rubber movement than that of the conventional tire when the tire rolls,
The internal energy loss was reduced, and the rolling resistance was reduced accordingly.

The same applies to the heat generation of the tire.

Here, the rolling resistance of the tire is pressed so that a predetermined load is applied to the tire on the surface of the steel drum having a drum diameter of 1.7 m, a predetermined speed, after running-in for about 45 minutes under air pressure, It measures running resistance.

Next, with respect to the tires of Comparative Example 1 and Example 1, the magnitude of the reaction force generated on the rotation axis of the tire running over the protrusion on the test course was measured, and the comparison data of the vibration riding comfort performance shown in Table 3 was obtained. Obtained.

This table shows the measurement results of Example 1 when the value of the reaction force of the tire of Comparative Example 1 is set to 100 as an index. The larger the index is, the better the vibration riding comfort performance is. Shows.

From Table 3, the example tires have vibration riding comfort performance equivalent to that of conventional products. This is because the large flexural deformation that the tire undergoes when riding over a projection on the road surface is absorbed and absorbed by the sidewall portion to maintain and improve the vibration riding comfort performance, but the tire of the present invention is fortunate in that respect. This is also because the carcass ply has a lower tension from the position of the maximum tire width having the highest absorption performance to the bead portion of the lower side wall region, and the tension distribution is such that flexural deformation can be absorbed relatively easily.

Next, Table 4 shows the values compared for the wet grip performance.

The wet grip performance is obtained by confirming the braking distance of a vehicle at a speed of 80 km / h by an actual vehicle test on a wet asphalt road, and the braking distance of the comparative example is 100 and the value of the example is displayed as an index. In this case also, the larger the index is, the better the wet grip performance is, and the example tires exhibit an advantageous braking force also in the wet grip performance, which is one of the important performances leading to the safety of the vehicle. is there.

This is largely due to the rigidity of the tread road, which means that when a car runs at high speed on a road surface with water accumulated,
The force that breaks through the resistance of water is high, and the critical speed of hydroplaning is correspondingly high, and the tire of the present invention provides a tire with high safety in this sense as well.

Furthermore, the high-speed durability of this type of tire is a performance that must be emphasized at the present when road conditions have been improved, and both tires were subjected to a high-speed durability test by the following test method. Shown in the table.

The high-speed durability test is carried out under the following conditions: Load: 3780 kg Initial internal pressure: 7.25 kg / cm ² Rim: 7.50 V At the speed level and the speed at the time of destruction by heat generated by running the drum running tester at the speed of step speed method. Evaluation is based on the length of running time. Also in this test, the tire of the embodiment of the present invention can clear the speed of 80 km / h, whereas the conventional tire can clear the speed of 70 km / h, which is much lower. This is because the product of the present invention exerts a high tension on the carcass from the buttress to the tread portion, so that the movement of the tread rubber is small, and the camber height C1 'is made large so that the rubber gauge B1 on both shoulders of the tread can be designed thin. It comes from the structure.

Next, regarding the wear resistance of the tread, the residual groove after running 50,000 km was measured by a comparison test by an actual vehicle test, and it was 1.00
The amount of tread wear per 0 km was compared. As shown in Table 6, the tire according to the present invention is 10% due to the contribution of the compressive strain acting on the tread contact surface above the ground and the more uniform contact partial pressure distribution.
It shows very good wear resistance.

[Advantages of the Invention] As described above, the radial tire of the present invention is provided with a carcass made of steel cords and a belt layer of high rigidity using the steel cords. The ratio of the radius of curvature CR1 in the range from the shoulder portion to the buttress portion and the radius of curvature CR2 in the range from the shoulder portion to the buttress portion of the carcass line 12 at the nominal maximum internal pressure is 0.70 ≦ CR2 / C.
Since R1 ≤ 0.95, when the carcass line of the sidewall part between the tread part and the bead part, which has relatively low rigidity, becomes a shape close to the free equilibrium profile due to the filling of internal pressure, it greatly affects the tire profile. The radius of curvature of the tread of the tire meridian can be increased.

As a result, a flat profile is obtained, so that a uniform ground contact pressure distribution can be obtained, and good grip and uniform wear can be obtained. Further, compression strain acts on the tread crown portion, which helps improve the cut resistance and wear resistance of the tread portion without impairing the steering stability of the vehicle.

Regarding the increase amount of the tread curvature radius of the tire meridional section described above, the curvature radius TR1 of the tire meridional section of the outer surface of the tread portion when the internal pressure is 5% and the curvature radius TR2 when the nominal maximum internal pressure is The ratio is usually 1.20 ≦ TR2 / TR1 ≦
It is set to 1.50, and the above-mentioned deformation is set as a preferable range.

Furthermore, the intersection where the carcass line 11 at 5% internal pressure and the radial line N1N1 'passing through the tread edge E1 at 5% internal pressure intersect
From the tire rotation axis YY 'of the intersection C2 where the radius RC1 from the tire rotation axis YY' of C1 and the carcass line 12 at the maximum nominal internal pressure and the radius line N2N2 'passing through the tread edge E2 at the nominal maximum internal pressure intersect The ratio RC2 / RC1 to the radius RC2 of
By making it larger than RX1, the range from the shoulder part of the carcass line 11 to the buttress part at 5% internal pressure, which is the internal pressure that restores the shape in the mold, can be freely set without thickening the shoulder rubber gauge B1. It can be arranged radially below the carcass line 12 having a nominal maximum internal pressure that approximates the equilibrium profile. As a result, the tire shape is greatly deformed in the range from the buttress portion to the tread portion without decreasing the high-speed durability of the tire due to the internal energy loss of rubber, the tension of the carcass in the range is increased, and the apparent rigidity is also increased. By increasing the size, the lateral rigidity can be increased in combination with the large rigidity of the tread portion.

Further, the distance RX1 from the tire rotation axis YY ′ at the intersection X1 between the carcass line 11 and the tire equatorial plane SS ′ when the internal pressure is 5%.
And the distance from the tire rotation axis YY ′ of the intersection point X2 between the carcass line 12 and the tire equatorial plane SS ′ at the nominal maximum internal pressure.
The ratio of RX2 is 1.000 ≤ RX2 / RX ≤ 1.005, and the intersection point X2 of the carcass line 12 with the nominal maximum internal pressure and the equatorial plane SS 'is the intersection point of the carcass line 11 and the tire equator SS' when the internal pressure is 5%.
The position is substantially the same as X1. Moreover, since the tire maximum width at the nominal maximum internal pressure does not substantially change from the tire maximum width at the 5% internal pressure, the carcass and the belt layer, together with the steel cord, extend from the tread portion to the buttress portion. It allows the above-mentioned deformation of the range.

As described above, the radial tire of the present invention can improve wear resistance, cut resistance, and the like without impairing other performances such as steering stability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the tire of the present invention, in which the solid line shows the nominal maximum internal pressure, the broken line shows the carcass line of 5% internal pressure, and the chain line shows the free equilibrium profile. FIG. 2 is a sectional view of a steel radial tire for trucks and buses, FIG. 3 is a sectional view showing a deformed state of a tire according to one embodiment of the present invention due to internal pressure, and FIG. 4 is a deformed state of a conventional tire due to internal pressure. Sectional view, FIG. 5 is a sectional view showing a carcass profile of a test tire, FIG. 6 (a) is a front view illustrating a tread cut resistance test device, and FIG. 6 (b) is an example of a jig thereof. Fig. 7 is a front view and a side view, Fig. 7 is a tire load-deflection curve diagram, Fig. 8 is a diagram illustrating a change in cornering force depending on a slip angle, and Fig. 9 is a line illustrating a relationship between speed and rolling resistance. FIG. 10 is a diagram for explaining the definition of the radii of curvature CR1 and CR2 of the carcass line.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 54-42706 (JP, A) JP 58-39503 (JP, A) JP 54-24762 (JP, B2)

Claims (1)

[Claims] 1. A carcass (1) provided with a steel cord which is folded back from a tread portion (5) to a side wall portion at a bead core (7) (7 ') of a bead portion and has a radical arrangement.
And a belt layer (3) using a steel cord disposed inside the tread portion (5) and outside the carcass (1) and inclined at a small angle in the tire circumferential direction, a radial tire having the nominal application of the tire. The radius of curvature TR1 of the outer surface of the tread portion (5) in the tire meridian section at the time of mounting on the rim and filling the air pressure corresponding to 5% of the nominal maximum air pressure and the nominal maximum air pressure are filled. The ratio of the outer surface of the tread portion (5) to the radius of curvature TR2 in the tire meridional section at the nominal maximum internal pressure is 1.20 ≦ TR2 / TR1 ≦ 1.50, and at the carcass line (11) at the internal pressure of 5%. Curvature radius CR1 in the range from shoulder to buttress
And the radius of curvature in the range from the shoulder to the buttress in the carcass line (12) at the nominal maximum internal pressure
The ratio with CR2 is 0.70 ≤ CR2 / CR1 ≤ 0.95, and when the internal pressure is 5%, the distance RX1 from the tire rotation axis YY 'of the intersection X1 between the carcass line (11) and the tire equatorial plane SS', and the nominal The carcass line (1
2) and the tire rotation axis YY ′ at the intersection X2 between the tire equatorial plane SS ′
From the distance RX2 to 1.000 ≦ RX2 / RX1 ≦ 1.005, and the intersection C1 where the carcass line (11) at 5% internal pressure and the radial line N1N1 ′ passing through the tread edge E1 at 5% internal pressure intersect An intersection point C2 where the radius RC1 from the tire rotation axis YY 'of the vehicle and the carcass line (12) at the nominal maximum internal pressure and the radius line N2N2' passing through the tread edge E2 at the nominal maximum internal pressure intersect
The ratio RC2 / RC1 to the radius RC2 from the tire rotation axis YY ′ is larger than the ratio RX2 / RX1, and the maximum tire width at nominal maximum internal pressure is the maximum tire width at 5% internal pressure. A radial tire characterized by being substantially unchanged.